The present invention relates to a dielectric filter, and more particularly, to an integrated type dielectric filter which can stop a frequency signal at a lower frequency area than a pass band as a reference band with a higher attenuation ratio, thus to perform adjustment of the attenuation ratio even the lower frequency area in a simple manner.
Generally, a dielectric filter has a plurality of dielectric blocks which are connected with each other, each dielectric block including a coaxial resonator therein, thereby obtaining a desired pass band characteristic, and an integrated type dielectric filter as an improved filter in a constructional respect has a single dielectric block having a plurality of coaxial resonators therein.
The integrated type dielectric filter used as a band passing filter is adapted for use in obtaining only a frequency signal of a desired channel band in a mobile communication equipment such as, for example, a car telephone, a portable telephone and the like which utilizes a high frequency band as a communication band. By this reason, the integrated type dielectric filter requires a small size, a light weight, and a high degree of impact resistance and also should need a band passing characteristic of about 20-30 MHz.
FIGS. 1 to 3 show first to third conventional integrated type dielectric filters, respectively. Firstly, the conventional integrated type dielectric filter as shown in FIG. 1 has a coupling hole 9 disposed between two resonant holes 7 and 8, to thereby adjust mutual inductance and mutual capacitance. In this case, a degree of coupling is dependent upon the size, length and position of the coupling hole 9. However, addition of the coupling hole 9 causes the molding of the dielectric filter to be difficult as well as a mechanical strength thereof to be deteriorated, such that there is a problem in that the conventional integrated type dielectric filter is not satisfied with the requirements of the existing mobile communication equipment. Secondly, the conventional integrated type dielectric filter as shown in FIG. 2A includes two resonant holes 7 and 8 which each have an inconstant inside diameter, that is, have the inside diameter being varied at a specific portion thereof, as shown in FIG. 2B, to thereby achieve the coupling of the resonant holes by a characteristic impedance difference caused due to the difference of the inside diameter of the resonant hole. When compared with the dielectric filter as shown in FIG. 1, the integrated type dielectric filter of FIG. 2A has an improved band passing characteristic, but there still remains a problem in that since the inside diameter of the small resonant hole is not constant, the manufacturing process becomes complicated and an uniform molding state can not be accomplished. Finally, the conventional integrated type dielectric filter as shown in FIG. 3A does not have any opening surface when compared with the above conventional dielectric filters and has a side surface of a dielectric block 1 on which a conductive material is covered to thereby form an electrode, and specific portions 17 and 18 within the interior of the resonant holes 7 and 8 whose electrodes are eliminated, as shown in FIG. 3B, thus to achieve the coupling state between the resonators. In the conventional dielectric filter as shown in FIG. 3A, however, there is a problem in that it is difficult that the electrodes placed at an arbitrary position of the internal surfaces of the small resonant holes 7 and 8 are accurately removed.
Moreover, as recently the interval between communication channels is gradually shortened, the dielectric filter should have a high attenuation characteristic and particularly, in the case where the dielectric filter is quite adjacent to a transmitting channel and/or a receiving channel, it should need a higher attenuation ratio at a specific frequency band.
For instance, in the case where the dielectric filter has the transmitting channel as a pass band, it should require a higher attenuation ratio at a lower frequency band than a pass band as a reference band, not to receive a signal of the receiving channel which is adjacent to the low frequency band. As discussed above, however, it is evident that the first to third conventional integrated type dielectric filters can not provide such the higher attenuation ratio.
Accordingly, an object of the present invention is to provide an integrated type dielectric filter which can stop a frequency signal at a lower frequency band than a pass band as a reference band with a higher attenuation ratio, thus to perform adjustment of the attenuation ratio even the lower frequency area in a simple manner.
Another object of the present invention is to provide an integrated type dielectric filter which can stop a signal of a desired frequency band at lower frequency band than a pass band as a reference band with a higher attenuation ratio, thus to perform adjustment of the attenuation ratio even the lower frequency area.
According to an aspect of the present invention, there is provided an integrated type dielectric filter including: a dielectric block comprising first and second surfaces facing to each other and a side surface disposed between the first and second surfaces, the second and side surfaces being substantially covered with a conductive material; a plurality of resonant holes disposed substantially parallel to penetrate the first and second surfaces of the dielectric block and being substantially covered with the conductive material on the internal surfaces thereof, each of the plurality of resonant holes forming a resonator; input/output terminals each comprising an electrode area isolated from the conductive material of the side surface of the dielectric block and for forming an electromagnetic coupling with the plurality of resonant holes; and at least one conductive pattern disposed at a predetermined distance from the end portion of each of said plurality of resonant holes on said first surface of said dielectric block, for forming the electromagnetic coupling between the adjacent resonators.
Preferably, the conductive pattern is disposed at a predetermined distance from the end portion of each of the plurality of resonant holes on the first surface of the dielectric block, along with the arranged direction of the plurality of resonant holes, for forming a coupling capacitance between the adjacent resonators and for forming a cross coupling capacitance between the resonators not adjacent. Accordingly, the dielectric filter can form a pass band having a low frequency area as the coupling inductance between the resonators is increased by the formation of the conductive pattern.
According to another aspect of the present invention, there is provided an integrated type dielectric filter including: a dielectric block comprising first and second surfaces facing to each other and a side surface disposed between the first and second surfaces, the second and side surfaces being substantially covered with a conductive material; a plurality of resonant holes disposed substantially parallel to penetrate the first and second surfaces of the dielectric block and being substantially covered with the conductive material on the internal surfaces thereof, each of the plurality of resonant holes forming a resonator; input/output terminals each comprising an electrode area isolated from the conductive material of the side surface of the dielectric block and for forming an electromagnetic coupling with the plurality of resonant holes; and a resonant frequency adjusting conductive pattern disposed to be extended from the side surface of the dielectric block toward the end portions of the resonant holes of the first surface on the dielectric block, for adjusting a resonant frequency of each of the resonators.